Hydrosilylation reaction involving addition reaction of a Si—H functionality compound to a compound having a carbon-carbon double or triple bond is a useful means for synthesizing organosilicon compounds and is also industrially important synthetic reaction.
Pt, Pd and Rh compounds are known as catalysts for the hydrosilylation reaction. Most often used among them are Pt compounds as typified by Speier catalysts and Karstedt catalysts.
One of problems associated with Pt compound-catalyzed reactions is that the addition of a Si—H functionality compound to terminal olefin entails side reaction or internal rearrangement of olefin. Since this system does not display addition reactivity to internal olefin, unreacted olefin is left in the addition product. To complete the reaction, the olefin must be used previously in excess by taking into account the portion that is left behind due to side reaction.
Another problem is low selectivity between α- and β-adducts depending on the identity of olefin.
The most serious problem is that all Pt, Pd and Rh as the center metal are very expensive noble metal elements. Since metal compound catalysts which can be used at lower cost are desired, a number of research works have been made thereon.
For example, reaction in the presence of iron-carbonyl complexes such as Fe(CO)5 and Fe3(CO)12 is known from Non-Patent Document 1. For this reaction, reaction conditions including a high temperature of 160° C., or light irradiation is necessary (Non-Patent Document 2).
Non-Patent Document 3 reports exemplary reaction of methylvinyldisiloxane with methylhydrogendisiloxane using an iron-carbonyl complex having a cyclopentadienyl group as ligand. In this reaction, dehydrogenation silylation reaction takes place preferentially.
Non-Patent Document 4 describes reaction using an iron catalyst having a pyridine ligand. A large excess of reducing agent (NaBHEt3) is necessary as reaction aid. Although PhSiH3 and Ph2SiH2 add to olefins, more useful trialkylsilanes, alkoxysilanes and siloxanes have poor addition reactivity to olefins.
Non-Patent Documents 5 and 6 report Fe complexes having a bisiminopyridine ligand. It is disclosed that they display good reactivity to alkoxysilanes and siloxanes under mild conditions. The reaction using these complexes, however, has several problems including low reactivity to internal olefin, use of sodium amalgam, which consists of water-prohibitive sodium and highly toxic mercury and requires careful handling, or use of water-prohibitive NaBEt3H during the synthesis of the complex, and low stability of the complex compound itself, which requires handling in a special equipment like glovebox and storage in nitrogen atmosphere.
On the other hand, a number of reports are made on hydrogenation reaction of olefins. For example, Non-Patent Document 7 reports hydrogenation by thermal reaction using Fe(CO)5 catalyst, and Non-Patent Document 8 reports hydrogenation by photo-reaction. However, the thermal reaction requires high-temperature (180° C.) and high-pressure (28 atm.) conditions, and the turnover count is as low as 0.5. It is not concluded that the catalyst has sufficient activity. Also the photo-reaction can take place even at room temperature, but a turnover count of 33 is still insufficient.
Non-Patent Document 9 reports exemplary reaction using an organoaluminum compound as reaction aid and an iron catalyst. A turnover count of 17 indicates low catalytic activity.
Non-Patent Document 10 reports exemplary reaction using a Grignard compound in combination with an iron chloride catalyst. The system allows reaction to run at room temperature, but requires high-pressure (20 atm.) conditions, and the turnover count is as low as 20.
Non-Patent Document 11 reports an iron catalyst having a phosphorus base compound as ligand. Although the system allows reaction to run at room temperature and a relatively low pressure (4 atm.), the reactants are limited to styrene and some alkenes, and the turnover count is not regarded sufficient.
Also, Non-Patent Document 5 cited above reports an exemplary iron catalyst having a bisiminopyridine ligand. Reactivity is satisfactory as demonstrated by a turnover count of 1,814 at room temperature and a relatively low pressure (4 atm.). This reaction suffers from problems including safety upon synthesis and stability of the relevant compound like the aforementioned iron complex having a bisiminopyridine ligand.
One known method for reducing carbonyl compounds is by using hydrogen in the presence of aluminum hydride, boron hydride or noble metal catalysts. For ketones and aldehydes among carbonyl compounds, there are known hydride promoters and hydrogenation noble metal catalysts which allow progress of reaction under mild conditions and are stable and easy to handle. For reducing carboxylic acid derivatives such as esters and amides, the main method uses strong reducing agents such as lithium aluminum hydride and borane (Non-Patent Document 12). However, since these reducing agents are flammable, water-prohibitive substances, they are awkward to handle. Also careful operation is necessary when the aluminum or boron compound is removed from the desired compound at the end of reaction. In addition, high-temperature/high-pressure hydrogen is necessary for the reduction of carboxylic acid derivatives.
There are reported many methods using methylhydrogenpolysiloxane or hydrosilane compound which is stable in air and easy to handle, as the reducing agent. For this reaction, addition of strong acids or Lewis acids is necessary as well as expensive noble metal catalysts. One recent report relates to reductive reaction of carbonyl compounds in the presence of low cost iron catalysts. In some examples, the catalyst is applied to reductive reaction of amides which requires rigorous conditions in the prior art. While illustrative examples of the iron catalyst are given in Non-Patent Documents 13 to 18, there is a desire to have high activity catalysts displaying a greater turnover count.
Also, examples of the iron complex compound having catalytic activity to three reactions: hydrosilylation reaction, hydrogenation reaction, and reductive reaction of carbonyl compounds, which have been reported heretofore, are only bisiminopyridine complexes by Chirik et al. (Non-Patent Documents 5, 6) and Fe(CO)5. On use of the complexes by Chirik et al., carbonyl compounds of ketone and aldehyde type can be reduced, but reduction of carboxylic acid derivatives is not achievable. On use of Fe(CO)5, reduction of amides as carboxylic acid derivatives with silanes is achievable, but requires a high temperature of at least 100° C. or light irradiation, and a long reaction time (9 to 24 hours), suggesting that reaction under mild conditions is difficult.